More shunt rigging [RE-wrenches]

[Bob Ellison, Alternative Energy Systems]

The owner wants to use a Navy surplus 0-500 amp dial readout for his tests.
It would be cool to have on the wall! We just need to figure out how to
double the range so 500 on the meter will actually be 1000 amps. My
suggestion was to just use a shunt and meter. He wants the dial cause it is
easy to read at a glance.

Learning more every day, thanks for the help.
Bob

-----Original Message-----
From:	Ray Walters [mailto:remotech at taosnm.com]
Sent:	Wednesday, December 20, 2000 1:18 PM
To:	RE-wrenches at topica.com
Subject:	Re: More shunt rigging [RE-wrenches]

Maybe this is a stupid question, but why don't they use a 1000A/ 100 mV
shunt from applied power with a Trimetric. It reads just the same as a 500
A 50mV shunt.

Ray
 At 09:26 AM 12/18/00 -0800, you wrote:
>>Slight difference between
>>two shunts will cause unequal current distribution, and the meter
>>will read the higher of the two ... I think!
>
>	Windy;
>
>	Remember, two shunts in parallel, connected with sufficiently heavy
>conductors, act as one resistance, therefore there will be only one
>voltage, the sum of the voltage drop across them both.
>	Look at it this way, if you parallel connect two batteries with large
>interconnects, then read the voltage of each battery, it will be the same
>on both right? At least it will be close enough for you to assume that they
>are both at the same voltage for practical purposes.
>	If you were really stressed about accuracy, I'd put the meter across the
>high side of one shunt and the low side of the other
>
>>The best way is to put a resistance in series with the meter.
>
>	I agree that one shunt is the way to go. I use a 50 mv/100 A shunt on my
>PV input, driving a remote 1mA meter movement in series with a 200 ohm,
>15-turn pot. I calibrated it by reading the output of the shunt with a DVM
>and transposing the reading to the meter, adjusting the pot to match. Works
>great. A 50 mv meter movement wouldn't work because the resistance in the
>wiring back to the metering position caused the meter to read low.
>	This brings up the case for custom shunts and meter movements. I have
>constructed many shunts using brass threaded rod in a variety of sizes, and
>used all manner of salvaged meter movements to provide metering for odd
>values or to make use of 'vintage' panel meters for custom installations.
>Try finding a 10, 15 or 30A shunt. Try loacting a shunt to match a 50uA
>meter movement.
>	One of my better projects was engineering and constructing a -30/0/+10
>shunt and meter that used off-the-shelf components and a standard 0-100uA
>meter movement that self-center-zeros when the current isn't going either
>direction.
>
>>Write a big " Multiply X 2 " on the meter.
>
>	Many meters have removable faces, I used a Brother Labelmaker to print new
>values for the graduations on the meter face, so it reads 0-100A instead of
>0-50.
>
>>The shunt will be fine as long as it doesn't carry 1000 amps long
>>enough to get hot.
>
>	Heating in the shunt isn't going to be much of a problem. At 1000A, a 50
>mv shunt is dissipating 1 watt, hardly enough to make it even warm. The
>larger factor would be the voltage drop in the circuit, and at .001 volt,
>even that seems insignificant.
>	Yours in theory,
>
>	-S
>
>
>
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 RE-wrenches at topica.com

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 http://www.topica.com/lists/RE-wrenches/

To unsubscribe send a message to: 
 RE-wrenches-unsubscribe at topica.com

To check out the other RE-Wrench participants:
 www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

___________________________________________________________
T O P I C A  http://www.topica.com/t/17
Newsletters, Tips and Discussions on Your Favorite Topics